1. Field of the Invention
The present invention relates to screen printing machines and, more particularly, to screen printing machines in which printing platens are moved around an endless path through successive printing stations.
2. Description of the Related Art
Screen printing machines of this type are known, for example, for printing T-shirts, and such machines usually comprise a plurality of printing stations, each provided with a printing screen, an inking and squeegee system for applying ink to the screen and a platen alignment system for locating the platens in position as the platens arrive, in succession, at each printing station.
In such machines, the platens are driven by means of an endless chain drive mechanism around their endless path on a machine bed. The alignment of each platen at each printing station has been effected by means of an alignment mechanism applying force to the platens in a direction extending transversely of the path of travel of the platens. This has the disadvantage that the force exerted by this alignment mechanism tends to force components of the machine frame at opposite sides of the path of travel apart from one another, thus adversely affecting the accurate positioning of the platens at the printing station during printing operations.
More particularly, the frames of screen printing machines are normally constructed of frame components which are bolted together and which, consequently, tend to flex out of shape when subjected to forces tending to urge the frame components apart from one another. However, for accurate printing at successive printing stations, it is necessary to ensure that each platen is accurately located in position during each printing operation.
In prior art printing machines, as each platen arrives at a printing station, it is pushed so as to slide horizontally, in a direction transverse to the path of travel of the platen, to urge a drive chain, provided for displacing the platen around the path, into abutment with a rail in order to register the platen for printing.
Since each of the platens is simultaneously forced so as to slide against friction into abutment this way, and since the forces acting on the platens are exerted transversely of the path of travel of the platens, the machine frame is thus subjected to these forces, at various positions, and consequently the components of the machine frame are deflected, thus adversely affecting the accuracy of the registration of the platens.